Silver diffusion transfer process with mercapto-purine antifoggant

ABSTRACT

Mercapto-substituted purines are utilized in diffusion transfer photographic processes to give positive transfer prints of high quality over a very broad range of processing temperatures.

United States Patent Johnson, Jr.

[ Feb. 15, 1972 SILVER DIFFUSION TRANSFER PROCESS WITII MERCAPTO-PURINE ANTIFOGGANT Edward J. Johnson, Jr., Tewksbury, Mass. Polaroid Corporation, Cambridge, Mass. Jan. 18, 1968 Int. Cl ..G03c 5/54 Field of Search ..96/29, 95, 109, 66.5

References Cited UNITED STATES PATENTS Land ..9s/ss Spath ..96/22 Blake.... ....96/29 Fry ..96/ 109 Knott ..96/6l Tregillus et al. ....96/58 X Goodchild et a1. ..96/29 Primary Examiner-Norman G. Torchin Assistant Examiner-Won H. Louie, Jr. Attorney-Brown and Mikulka and Sybil A. Campbell ABSTRACT Mercapto-substituted purines are utilized in difiusion transfer photographic processes to give positive transfer prints of high quality over a very broad range of processing temperatures.

12 Claims, No Drawings BACKGROUND OF THE INVENTION This invention relates to photography and,,more particularly, relates to diffusion transfer processes wherein an exposed silver halide emulsion is developed and an image-wise distribution of unexposed silver halide is formed and transferred, at least in part, to an image-receiving layer.

In silver diffusion transfer processes, a latent image in a photoexposed silver halide emulsion is developed with a silver halide developing agent in the presence of a silver halide solvent. Almost simultaneously with the development of the latent image, the silver halide solvent reacts with the silver halide in the unexposed and undeveloped areas of the emulsion to form a soluble, diffusible silver complex. The solublesilver complex is, at least in part, transferred to an image-receiving stratum where the silver thereof is precipitated to form a;positive print.

It is desirable that such'processes operate to give prints of .good quality over a wide temperature range. In a diffusion transfer process performed at'elevated temperatures, the reactions of solution, transfer and development which are balanced at 70 F. are accelerated nonuniformly. The photographic resultof such behavior is aprint of low contrast with grey background instead of rich blacks. The'highlights will be dull and grey with no crispness."

It has been proposed to counteract these effects by employing certain compounds used in conventional Tray or wet development photography to'counteract thetendency of a silver halide emulsion to fog, i.e., to become developable without photoexposure, when developed at temperatures above room temperature. (The term antifoggants has frequentlybeen used as a class designationfor compounds found to be useful in counteracting such fogging tendencies.) These compounds frequently are not suitable for use in diffusion transfer processes and, if effective under high temperature-rapid development conditions in these: processes, they usually have an adverse effect on the quality of prints produced in the cold. For example, transfer prints processed at temperatures slightly above freezing tendto have excessive contrast with poor definition ofdetail in the shadows.

SUMMARY OF THE INVENTION It is, therefore, the primary object of the present invention to provide diffusion transfer processes and processing compositions useful therein that produce positive prints having improved contrast and whiter highlights at processing temperatures ranging from about 34 F. up to and in excess of 100 F.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

It has now been found according to the present invention that the above and other objects may be accomplished if the diffusion transfer process is carried out in the presence of a purine compound containing at least one free mercapto group attached to a carbon atom. As used herein, mercapto is intended to include -'SH and the ammonium and alkali metal salts thereof.

in US. Pat. No. 2,956,876, mercapto-substituted purines have been disclosed as useful for'preventing color fog in conventional color reversal photographic processes which involve a multistep procedure including black and whitedevelopment followed by reversal exposure, color development, fixing, washing at various intervals, and so forth. It is quite unexpected that such compounds will-perform in diffusion transfer processes where there are balanced and competing developing and solution reactions to give prints having improved contrast and improved highlights. Moreover, that these compounds will perform in diffusion transfer processes togive increased and comparable effective film speeds (exposure index ratings) at both high and low temperatures is not only unexpected but unique and permits the production of prints of improved quality over a very broad temperature range.

The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and to compositions possessing the features and properties which are exemplified in the following detailed disclosure and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the natureand objects of the invention, reference should be had to the following detailed description.

DESCRIPTIONOF THE PREFERRED EMBODIMENTS The present invention is primarily concerned with the processing, in the presence of a mercapto-substituted purine, of an exposed silver halide emulsion to give directly and, without .further exposure, a positive print obtained by the development of an exposed emulsion and by the transfer of at least aportion of the silver of the unexposed regions of said emulsion to a suitable image-receiving element, the silver producing a visible image upon precipitation on said element.

' -In one form of the process, the development of the latent image and the transfer and precipitation of the silver from the undeveloped areasof the silver halide emulsion occur almost simultaneously. A liquid processing composition is so applied to-thesurface of a photosensitive silver halide element as to be absorbed-in part into the emulsion of said element and this single liquid application develops the exposed silver halide and causes the formation of asoluble silver complex with the remaining undevelopedsilver halide. The processing composition is best applied in a thin, uniform, relatively viscous. layer, for example,-by being spread on thCBIIII-IISIOILIH a preferred form of the process, the liquid processing composition is spread between the photosensitive and image-receiving elements as described in detail in US. Pat. No. 2,647,056 issued July 28, -l953toEdwin H. Land.

In carrying out the present process of producing diffusion transfer prints of good pictorial quality over a wide temperature range, the purines that maybe used contain at least one mercapto. group attached to a carbon atom of the purine nucleus. A single mercapto-substituted purine may be employed, or if desired, a mixture of two or more such compounds may be used. For achieving the benefits of the present invention most efficiently, the purine(s) is preferably added to the liquid processing composition.

The class of mercapto-substituted purines particularly useful for practicing the present invention. have at least one tautomeric form that may be represented by the following structural formula:

- e.g.,- sodium and potassium. Foruse in the aqueous alkaline processing compositions commonly used inzdiffusion transfer processes, R, R and R each:are generally selected from the group consisting'of hydrogen, amino, hydroxyl, alkyl, aryl and --"SM wherein M is a member selected from the group consisting of hydrogen, ammonium and an alkalimetahtat.least one -of said R, R 'and R being SM. It will be understood that the R substituents are selectedsuch that the compound will be soluble inthe particular processing composition employed.

Txei a frths Q eu th t ma stn d are 8-mereapto purine fi-mercapto purine H W H H l L 2,6-dimercapto purine l5 H H l Ll N 6-hydroxy-2-mercapt0 purine H N SH 6-hydroxy-3-mercapto purine H N l H H i L N 2-mercapt06,8-d.ihydroxy purine l i H K.

fi-aminoe-mereapto purine 5 0 H N l 5 5 HzN-KN 2-an1lno-6-mercapto purine 2'memaptmfi-amma purine T H H H L 2-untlno-6-hydroxy-8-mercapto amine The purine compounds may be used advantageously over a relatively wide range of concentrations with the minimum concentration being that amount sufficient to give satisfactory prints at both elevated temperatures and in the cold. The 0ptimum concentration will depend upon the particular emulsion, the processing composition, etc., and can readily be determined in each case. When the purine compound is incorporated into the liquid processing composition, it is ordinarily added in amounts ranging between about i and 4 grams per liter of composition.

As indicated above, the liquid processing composition contains certain ingredients, some of which may be added wholly or in part to the composition during the spreading thereof as by being dissolved into the composition from the photosensitive and/or image-receiving elements, but which are most conveniently introduced therein prior to spreading. The essential ingredients are (a) a silver halide developing agent(s), i.e., a substance capable of reducing the exposed silver halide of the latent image to silver, (b) a silver halide solvent(s), i.e., a substance capable of forming with the substantially unexposed silver halide a silver complex which is soluble in the particular liquid vehicle used for the processing composition and (c) a mercapto-substituted purine(s) as defined above for increasing the effectiveness of the process for producing positive transfer prints of good pictorial quality at processing temperatures of from slightly above freezing up to temperatures of the order of F.

In the processing composition, any suitable developing agent(s) and silver halide solvent(s) may be employed. Among the developing agents that may be employed are benzene and naphthalene compounds having hydroxyl and amino substituents ortho or para to one another, e.g.,

hydroquinone, chlorohydroquinone, bromohydroquinone, toluhydroquinone, p-methyl aminophenol sulfate, and pyrogallol.

The silver halide solvent may be selected from any of those known to the art. Particularly useful silver halide solvents include the alkali thiosulfates, e.g., sodium thiosulfate and cyclic imides, e.g., uracil.

Preferably, the processing composition also contains a thickening agent to increase and impart the desired viscosity characteristics. A viscosity of from 1,000 to 200,000 centipoises at a temperature of 20 C. has been found satisfactory for permitting the composition to be readily controlled during and after spreading. Illustrative of suitable thickening agents are carbohydrates, e.g., starch; gums, e.g., gum arabic; and plastic materials, e.g., hydroxyethyl cellulose, sodium carboxymethyl cellulose and the sodium salts of polyacrylic and polymethacrylic acids.

Additionally, the composition contains an alkali, e.g., sodium hydroxide, and may contain a restrainer, e.g., potassium bromide; a preservative, e.g., sodium white; or other adjuvants as conventionally used in diffusion transfer processes. The developing agent, silver halide solvent and any adjuvant employed, such as a thickener, are used in conventional amounts to achieve the desired effects.

As mentioned hereinabove, in a preferred embodiment of the present invention the processing composition is spread in a uniformly thin layer between the superposed surfaces of a photoexposed silver halide emulsion and an image-receiving element, which procedure may be accomplished, for instance, by advancing the elements between a pair of pressure-applying rollers. In such a process, the liquid processing composition, including the developing agent, the silver halide solvent and the mercapto-substituted purine may be conveniently provided in a rupturable container attached to either the photosensitive element and/or image-receiving element such that when the elements are superposed the container is so positioned as to be capable upon rupture of releasing its contents in a substantially uniform layer between and in contact with the surfaces of each of the elements.

Such containers are preferably inexpensive and disposable, and so constructed as to be capable of retaining the processing composition therein for relatively long periods of time without vapor loss or oxidation. Examples of containers that may be used for this purpose are described in U.S. Pat. No. 2,634,886 issued to Edwin H. Land. Generally, the containers are fabricated from a blank comprising a three-ply sheet material including respectively an outer lamina of a strong deformable sheet material, e.g., kraft paper; an intermediate lamina impervious to the vapor of the processing composition, e.g., a metal foil; and an inner lamina inert and impervious to the processing composition, e.g., a thermoplastic resin layer. The container blank is folded upon itself and sealed in such a manner as to provide a container having a fluid-containing capacity and a sealed marginal edge which may be substantially unsealed throughout a predetermined portion of its length upon application of stress to the container.

The photosensitive element may comprise any of the commercially available silver halide emulsions such as gelatino silver chloride, chlorobromide, chloriodide, chlorobromoiodide and bromoiodide emulsions which may be coated on any suitable support, for example, glass, paper and plastic film base. The present compositions and processes, however, areparticularly useful for improving the results obtained with the higher-speed photosensitive emulsions.

The emulsions may be chemically sensitized with sulphur compounds such as thiourea; with reducing substances such as stannous chloride; with noble metals such as gold or platinum; with amines and with quaternary ammonium compounds. Also, the emulsion may contain accelerators, coating aids and other such addenda where desired.

The image-receiving element may be any of those conventionally used in diffusion transfer processes and comprises a suitable support, such as baryta paper, which may have an outer layer formed of a natural or synthetic resin or a mixture thereof, which layer comes into contact with the processing composition. The image-receiving element preferably contains silver precipitating agents or nuclei since the presence of such materials during the diffusion transfer process has a desirable effect on the amount and nature of the silver precipitated in the formation of the positive print. Examples of materials suitable for this purpose are the metallic sulphides and selenides, thiooxalates, thioacetamides and colloidal metals disclosed in U.S. Pat. No. 2,698,237 issued Dec. 28, 1954 to Edwin H. Land. Also, as disclosed in this patent, it is desirable to provide on the support a continuous film consisting of submacroscopic agglomerates of minute siliceous particles as a vehicle for the silver precipitating agents or nuclei to enhance the aggregation of silver into its most effective form.

To illustrate the efficacy of mercapto-substituted purines in producing transfer prints of more uniform quality at different temperatures, a number of such compounds were evaluated in the hot, in the cold and at room temperature in the same silver halide diffusion transfer process using the same processing composition, the same photosensitive element (silver iodobromide emulsion carried on a paper base) and the same imagereceiving element (colloidal silica containing silver precipitating nuclei carried on a paper base in accordance with the teachings of the aforementioned U.. P at. w

The alkaline processing composition employed comprised the following ingredients:

Water I000 cc. Hydroxyethyl cellulose 43.7 g. Sodium sulfite 3l.l g. Sodium hydroxide 50.7 g. Sodium thiosulfate pentahydrate 88.5 g. Triaminophenol dihydrochloride 5.9 g. t-butyl hydroquinone l6.8 g.

In formulating the above, the hydroxyethyl cellulose was dissolved in water with stirring at room temperature. Thereafter, the remaining ingredients except for the developing agents were stirred into the solution and finally, the triaminophenol and hydroquinone were dissolved therein.

A series of the above-described photosensitive elements were exposed to the same subject matter under identical conditions and then advanced in superposed relationship with the aforementioned image-receiving elements between a pair of pressure-applying rollers to spread the liquid processing composition between the elements in a layer about 1.8 mils thick. After an imbibition period of 60 seconds in the cold and 10 seconds at both room temperature and in the hot, the photosensitive and irnage-receiving elements were separated to uncover the positive transfer prints.

The particular purine compounds employed and designated A-K were as follows:

B-mercapto purine 6-mercapto purine 2,6-dimercapto purine 2,6,8-trimercapto purine 6-hydroxy-2-mercapto purine 6-hydroxy-8-mercapto purine 2-mercapto-6,8-dihydroxy purine 6-amino-8-mercapto purine 2-amino-6-mercapto purine J 2-mercapto-6-aminopurine K 2-amino-6-hydroxy-8-mercapto purine The concentration of purine compound used together with the exposure rating and density characteristics of the prints produced with each compound are given in the following table. The control consisted of the above processing composition without a mercapto-purine present.

Exposure rating is given in terms of Diffusion Transfer Exposure Index. This term as used herein refers to the exposure index to which an A.S.A. calibrated exposure meter should be set to determine the proper exposure to which a negative for use in a silver diffusion transfer process must be subjected in order to obtain a satisfactory positive print and may be based on a curve relating original exposure of the negative to the density in the resultant positive. Conventionally, the Diffusion Transfer Exposure Index of a silver halide transfer process is determined by plotting a characteristic curve of the reflection density of the positive as a function of the log exposure of the negative, determining the exposure in meter-candle-seconds atthe point on this curve corresponding to a density of 0.50,

and dividing the constant, 4.0, by the exposure so determined.

, TABLE I Pun Coneentra- Diflusion transfer exposure index Maximum density Minimum density compound gins/10 cc. Cold l Room b Hot n Cold n Room b Hot 0 Cold 5 Room b Hot n Control 960 368 1. 1. 61 l. 40 0. 01 0.23 0. 43

A 04 1, 300 2, 360 1, 760 1. 1. 53 1. 47 O. 00 0.00 0. 00 04 2, 250 2, 400 1, 880 1. 35 1.44 1. 32 0.00 0. 00 0. 01 .04 2, 050 2, 640 2, 1. 47 1.47 1. 46 0. 00 0. 00 0. 01 02 1, 680 1, 680 1, 240 1. 46 1. 49 1. 42 0.00 0. 01 0. 00 04' 1, 640 2, 500 2, 1. 44 1. 58 1. 46 0. 01 0. 00 0. 01 04 1, 760 2, 780 2, 100 1. 36 1 50 1. 40 0. 01 0. 01 0. 02 02 1, 450 1, 480 1, 240 1. 39 1. 56 1. 46 0.01 0. 02 0. 02 02 720 880 800 1. 57 1. 54 1. 48 0. 02 0. 03 0. 02 02 1, 210 1, 300 1,180 1. 44 1.59 1. 52 0.01 0. 01 0. 06 03 1,360 1, {:10 1, 240 1.50 1. 52 1. 39 0. 00 0. 00 0. 06 04 1, 210 960 l, 360 1. 49 1. 53 1. 50 0.02 0. 04 0.02

It will be noted from the data set forth in the table that transfer prints produced in the presence of a mercapto-substituted purine exhibited low minimum densities at all three temperatures and showed a substantial decrease in maximum The results set forth in Table ll, like those presented in Table I, clearly show that in the presence of a mercapto-purine, improved film speeds are obtained over the entire temperature range and further, that the speeds are relatively density loss between room and high temperature processing. It uniform at all three temperatures. Also, it is readily apparent will be noted further that the Diffusion Transfer Exposure In that prints of improved highlights are obtained at the higher dices obtained in the presence of each pun'ne compound are temperatures in the presence of a mercapto-purine as very similar at the various processing temperatures as comreflected by the substantial reduction in minimum densities at pared to the exposure indices of the control prints, wherein both room temperature and elevated temperatures. the exposure index in the cold is more than 3% times that at 10 It will be apparent that it is within the scope of the present room temperature and more than 2% times that at elevated invention to modify the processing compositions described temperatures. This improvement in high-temperature density above by altering the relative proportions of the ingredients characteristics, together with the uniformity in exposure and/or by the substitution of developing agents, silver halide ratings over the entire temperature range is an unusual com- Solvents. alkalis and so forthbination of properties which ensures the production of high Slime Certain changes y be made in the above P quality transfer prints at low temperatures as well as at high and compositions without departing from the scope of the temperatures. present invention, it is intended that all matter contained in Us P N 2,704 721, i d to Ed i H L d on M the above description be interpreted as illustrative and not in a 22, 1955, proposes to improve high-temperature performance limiting Senseof diffusion transfer processes by using certain five-membered what is claimed is: heterocyclic compounds, of which S-nitrobenzimidazole In a diffusion transfer P Q which compfise? P nitrate may be considered illustrative. For comparison purof hevelopihg exposeqshver hahde of a Photosehsmve poses, S-nitrobenzimidazole nitrate was added to the above halide hwltha Silver hal P agent and form processing composition at a concentration of 0.04 grams per mg h lmagewlse dlsthbuhoh a sohlhle Sliver mp y l0 cc. (cubic centimeters). The resulting composition was reactmg uhelfposed hver hahde of sald'photosehsmve used to prepare a series of prints at the three different teml F trahsffimhg at least a p peratures given above according to the same procedure and f 1 lmagejwlse dlstflbutloh 531d sllvehcPmplex y dlffu' using the same photosensitive and image-receiving elements. Slon alkahne soiuuon to ?8 element and The exposure indices obtained in the cold, at room temperaf an Image ltlcqrporatmg from Sam mfnsferred ture and in the hot were 1075, 740 and 596, respectively. The Sllver complex sald g e i ng ment. the improvemaximum and minimum densities at the ditferent temperamam whch comprfses cnducfmgald P Q h Pmsence {mes 0 0 0 0 F) were L10, 156, of at least one purine soluble in said alkaline solution selected L43 and 0.01, 0. l4, 0.21 respectively. From these results, it is from those represented by the formula: readily apparent that the purines of the present invention per- 35 R H form much better over the entire temperature range and especially in the cold than those previously proposed compounds R represented by the above benzimidazole. Though previous 1 1- compounds, such as S-nitrobenzimidazole nitrate, give im- R L N roved results at the higher tem eratures, it is customary to iise other additives in combinati n with such compounds for I Q' R2 and R3 F each Selected from the group obtaining improved results in the cold. In contrast, the mer- 515mg of hydmgem ammo hydroxyl yh my] and SM capto purines perform well at both high and low temperatures wherem, M 15 selected the group conslstmg P y g in the absence of additives. ammonium and an alkali metal, at least one of said R and In another test, 2-amino-6-hydroxy-8-mercapto purine R bemg a trnsfer Image having "P (compound K) was added in an amount of 003 grams per 10 contrast and winter highlights 15 produced at processing tem. cc. to an alkaline processing composition which comprised the ggi g rangmg from about 34 up to and m excess followmg' 2. A process according to claim 1 wherein said purine is 8- Potassium hydroxide l56.5 g. mercapto purme' Um 800 3. A process according to claim 1 wherein said purine IS 6- Natrosol 250 (trade name of 50.0 g. mercapto P1111116. "mules CO'P- f y x- 4. A process according to claim 1 wherein said purine is 2,6- 322E221? dimercapmpmne- N N-dimcthoxyethyl-hydroxylamine 0,0 m 5. A process according to claim 1 wherein said purine is Water 1000.0 cc. 2,6,8-trimercapto purine.

6. A process according to claim 1 wherein said purine is 6- Using this composition, a series of prints were prepared at h d .2- i the three different temperatures given above using the same 7 A process acsording to l i 1 h i id purine i 6- procedure except that the imbibition time was 45 seconds at h d xy-ii-m a m i room temperature and in the hot and 120 seconds in the cold. 8 A process according to l i 1 h i id purine i 2- The photosensitive element used comprised a gelatino silver er a t -fi-dihydm purine, iodobromide emulsion on a paper base, and the image-receiv- 9. A process according to claim 1 wherein said purine i 6. ing element comprised a cellulose diacetate layer containing a amino-8-mercapto purine. nickel sulfide precipitant coated on a paper e and 10. A process according to claim 1 wherein said purine is 2- hydrolyzed to a depth of 0.00005 inch. amino-6-mercapto purine.

The exposure index and maximum and minimum densities 11. A process according to claim 1 wherein said purine i 2- for the prints obtained are given in Table II wherein the conmercapto--amino purine. trol represents prints prepared with the processing composi- 12. A process according to claim 1 wherein said purine is 2- tion without mercapto-purine present. amino-6-hydroxy-8-mercapto purine.

TABLE 11 Difiusion transfer exposure index Maximum density Minimum density Sample Cold Room Hot Gold Room Hot Cold Room Hot Control 1,120 800 1,760 1. 47 1.60 1.46 0.01 0.14 0.16 Compound K... 3, 3, 200 3,500 1. 61 1.49 1. 65 0.01 0. 02 0.02 

2. A process according to claim 1 wherein said purine is 8-mercapto purine.
 3. A process according to claim 1 wherein said purine is 6-mercapto purine.
 4. A process according to claim 1 wherein said purine is 2,6-dimercapto purine.
 5. A process according to claim 1 wherein said purine is 2,6,8-trimercapto purine.
 6. A process according to claim 1 wherein said purine is 6-hydroxy-2-mercapto purine.
 7. A process according to claim 1 wherein said purine is 6-hydroxy-8-mercapto purine.
 8. A process according to claim 1 wherein said purine is 2-mercapto-6,8-dihydroxy purine.
 9. A process according to claim 1 wherein said purine is 6-amino-8-mercapto purine.
 10. A process according to claim 1 wherein said purine is 2-amino-6-mercapto purine.
 11. A process according to claim 1 wherein said purine is 2-mercapto-6-amino purine.
 12. A process according to claim 1 wherein said purine is 2-amino-6-hydroxy-8-mercapto purine. 